The present invention relates to an air-conditioning system, which is provided with an engine for driving the vehicle and a compressor driven by a motor, and its control method.
Recently, to attain fuel efficiency of a vehicle, an idle stop control, which automatically stops an engine during an idle stop such that the vehicle stops moving at a red traffic light, is gradually adopted to vehicles. Japanese Unexamined Patent Publications No. 11-147424 and No. 2000-142091 disclose an air-conditioning system, a compressor of which is driven by a motor so as to air-condition during a stop of the engine.
A battery or a power source of the motor is charged by a generator, which is actuated by the engine. The amount of electric power accumulated in the battery decreases while the motor is driving the compressor during the stop of the engine. As the amount of electric power accumulated in the battery decreases, the engine starts to charge the battery. Therefore, the above-mentioned procedure for controlling an air-conditioning system, which does not consider the fuel efficiency, prevents in a short time the idle stop control or a device for improving the fuel efficiency from running efficiently. Accordingly, the motor needs to drive the compressor in view of power consumption of the motor.
In a hybrid type compressor, which is driven by one of the engine and the motor, as the motor is demanded for generating driving power equivalent to the engine, the motor becomes relatively large, and cannot mount the motor in an engine room. Incidentally, if a drive source of the compressor is the motor only, the arrangement of those units is not limited to the inside of the engine room, but may be the inside of a trunk room. Accordingly, in this hybrid type compressor, small motor is generally employed. Therefore, as the motor drives the compressor, an excessive load cannot be allowed to act on the motor.
The present invention addresses the above-mentioned problems traceable to idle stop control by restraining load torque of a compressor.
According to the present invention, an air-conditioning system for a vehicle, including a refrigerant circuit and an engine, has a battery, a compressor, an electric motor and a load torque control mechanism. The battery supplies electric power. The compressor is operative to compress refrigerant gas for the air-conditioning system. The electric motor is electrically connected to the battery. The motor is driven due to the electric power, and is operatively coupled to drive the compressor when the motor is energized. The load torque control mechanism responsive to the operating condition of the engine to control the load torque of the compressor below a predetermined value during times when the motor is driving the compressor.
Accordingly, while the motor is driving the compressor during the stop of the engine, power consumption of the motor is reduced and a load on the motor is decreased.
The present invention also provides a method for controlling an air-conditioning system for a vehicle, having an engine, the system including a compressor in a refrigerant circuit and an electric motor for driving the compressor. The method includes sensing the operating condition of the engine, and maintaining the load torque of the compressor below a predetermined value upon sensing a given operating condition of the engine.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.